Teac-EU-34-HT-Service-Manual电路原理图.pdf

SERVICE MANUAL EU-34HT 34cm CTV Effective: January, 1999 EU34HTSERV RadioFans.CN 收音机爱 好者资料库 1 CONTENTS Contents . 1 Safety Precautions . 2 TV Set switched off . 2 Measurements . 2 PERI-TV SOCKET . 2 SCART 1. 2 INTRODUCTION . 2 SMALL SIGNAL PART WITH TDA884X . 2-3 TUNER. 4 SOUND OUTPUT STAGE TDA2614 . 4 VERTICAL OUTPUT STAGE WITH TDATDA8356 . 4 VIDEO OUTPUT AMPLIFIER TDA6107Q. 4 POWER SUPPLY (SMPS) . 4 MICROCONTROLLER SDA545X . 5 SERIAL ACCESS CMOS 8K (1024*8) EEPROM ST24C08. 5 SAW FILTERS . 5 IC DESCRIPTIONS AND INTERNAL BLOCK DIAGRAM . 5 TDA8840/TDA8842 . 5-6 UV1316/UV1336 . 7 TDA2614 . 7-8 TDA8356 . 8 TDA6107Q. 8 MC44604 . 9 SDA545X. 9-11 ST24C08. 11 G1965M . 11 AK26 CHASSIS MANUAL ADJUSTMENT PROCEDURE . 11 For Adjust Settings. 11 WHITE BALANCE ADJUSTMENT . 11 AGC ADJUSTMENT . 11 IF-PLL NEGATIVE ADJUSTMENT . 12 4 : 3 HORIZONTAL SHIFT ADJUSTMENT . 12 4 : 3 VERTICAL SLOPE ADJUSTMENT. 12 4 : 3 VERTICAL AMPLITUDE ADJUSTMENT . 12 4 : 3 S-CORRECTION ADJUSTMENT . 12 4 : 3 VERTICAL SHIFT ADJUSTMENT . 12 For Option Settings. 12 OPTION 00 . 12-13 OPTION 01 . 13-14 OPTION 02 . 13 OPTION 03 . 14 OPTION 04 . 14 OPTION 05 . 14 OPTION 06 . 14 OPTION 07 . 15 GENERAL BLOCK DIAGRAM OF CHASSIS AK26 . 16 ELECTRONIC COMPONENT PART LIST . 17-18 RadioFans.CN 收音机爱 好者资料库 2 DO NOT CHANGE ANY MODULE UNLESS THE SET IS SWITCH OFF The mains supply side of the switch mode power supply transformer is live. Use an isolating transformer. The receivers fulfill completely the safety requirements. Safety precautions: Servicing of this TV should only be carried out by a qualified person. - Components marked with the warning symbol on the circuit diagram are critical for safety and must only be replaced with an identical component. - Power resistor and fusable resistors must be mounted in an identical manner to the original component. - When servicing this TV, check that the EHT does not exceed 26kV. TV Set switched off: Make short-circuit between HV-CRT clip and CRT ground layer. Short C804 (150mF) before changing IC802 or other components in primary side of SMPS. Measurements: Voltage readings and oscilloscope traces are measured under following conditions. Antenna signal 60dB from colourbar generator. (100% white, 75% colour saturation) Brightness, contrast, colour set for a normal picture. Mains supply, 110VAC, 60Hz. PERI-TV SOCKET SCART 1 (SC050) 1Audio right output0.5Vrms / 1K 2Audio right input0.5Vrms / 10K 3Audio left output0.5Vrms / 1K 4Ground AF 5Ground Blue 6Audio left input0.5Vrms / 10K 7Blue input0.7Vpp / 75ohm 8AV switching input0-12VDC /10K 9Ground Green 10- 11Green input0.7Vpp / 75ohm 12- 13Ground Red 14Ground Blanking 15Red input0.7Vpp / 75ohm 16Blanking input0-0.4VDC, 1-3VDC / 75ohm 17Ground CVS output 18Ground CVS input 19CVS output1Vpp / 75ohm 20CVS input1Vpp / 75ohm 21Ground 1. INTRODUCTION 11AK26 is a 90 chassis capable of driving 14? tubes at appropriate currents. The chassis is capable of working in PAL M, PAL N, PAL B/G and NTSC M. The sound system is capable of giving 2.5 watts RMS output into a load of 16 ohms. 2. SMALL SIGNAL PART WITH TDA884X The TDA8840/8842/8844 combine all small signal functions required for a colour TV receiver, except tuning. 2.1. Vision IF amplifier The IF-amplifier contains 3 AC-coupled control stages with a total gain control range which is higher than 66dB. The sensitivity of the circuit is comparable with that of modern IF-IC? s. The video signal is demodulated by means of a PLL carrier regenerator. This circuit contains a frequency detector and a phase detector. The AFC output is obtained by using the VCO control voltage of the PLL and can be read via the IC-bus. For fast search tuning systems the window of the AFC can be increased with a factor 3. The setting is realised with the AFW bit. Depending on the type the AGC-detector operates on top-sync level (single standard versions) or on top sync and top white-level (multi standard versions). The demodulation polarity is switched via the IC-bus. The AGC detector time-constant capacitor is connected externally. This mainly because of the flexibility of the application. The time-constant of the AGC system during positive 3 modulation is rather long to avoid visible variations of the signal amplitude. To improve the speed of the AGC system a circuit has been included which detects whether the AGC detector is activated every frame period. When during 3 frame periods no action is detected the speed of the system is increased. For signals without peak white information the system switches automatically to a gated black level AGC. Because a black level clamp pulse is required for this way of operation the circuit will only switch to black level AGC in the internal mode. The circuits contain a video identification circuit which is independent of the synchronisation circuit. Therefore search tuning is possible when the display section of the receiver is used as a monitor. The ident output is supplied to the tuning system via the IC-bus. The video ident circuit can be made less sensitive by means of the STM bit. This mode can be used during search tuning to avoid that the tuning system will stop at very weak input signals. 2.2. Video Switches The circuits have two CVBS inputs (internal and external CVBS) and Y/C input. When the Y/C input is not required the Y input can be used as third CVBS input. The selection of the various sources is made via the IC-bus. The circuit has one CVBS output. 2.3. Sound Circuit The sound band pass and trap filters have to be connected externally. The filtered intercarrier signal is fed to a limiter circuit and is demodulated by means of a PLL demodulator. This PLL circuit tunes itself automatically to the incoming carrier signal so that no adjustment is required. The volume is controlled via the IC-bus. The deemphasis capacitor has to be connected externally. The non-controlled audio signal can be obtained from this pin. The FM demodulator can be muted via the IC-bus. This function can be used to switch-off the sound during a channel change so that high output peaks are prevented. The TDA8840/8842 contain an automatic volume levelling (AVL) circuit which automatically stabilises the audio output signal to a certain level which can be set by the viewer by means of the volume control. This function prevents big audio output fluctuations due to variations of the modulation depth of the transmitter. The AVL function can be activated via the IC-bus. 2.4. Synchronisation circuit The sync seperator is preceded by a controlled amplifier which adjusts the sync pulse amplitude to a fixed level. These pulses are fed to the slicing stage which is operating at 50% of the amplitude. The separated sync pulses are fed to the first phase detector and to the coincidence detector. This coincidence detector is used to detect whether the line oscillator is synchronised and can also be used for transmitter identification. The first PLL has a very high statical steepness so that the phase of the picture is independent of the line frequency. The horizontal output signal is generated by means of an oscillator which is running at twice the line frequency. Its frequency is divided by 2 to lock the first control loop to the incoming signal. The time-constant of the loop can be forced by the IC-bus (fast or slow). If required the IC can select the time-constant depending on the noise content of the incoming video signal. To protect the horizontal output transistor, the horizontal drive is immediately switched off when a power-on-reset is detected. The drive signal is switched-on again when the normal switch-on procedure is followed. Via the IC-bus, adjustments can be made of the horizontal and vertical geometry. The vertical sawtooth generator drives the vertical output drive circuit which h